Switches and other controls for electronic devices are typically discrete component assemblies requiring multiple parts. A higher number of parts generally requires an increase in the size of the device and the space required to house the device as well as the cost. Furthermore, with an increase in number of parts there is a decrease in reliability. Discrete controls with multiple parts are difficult to interconnect to an electronic device. The discrete controls require separate interconnections which must be made from the control component to the rest of the electronic device, usually contained on a PCB (printed circuit board). The interconnections require flex circuits, hand soldered joints and wire connections, all which increase the cost and size of the electronic device. These interconnections consume valuable space that is often premium in small electronic devices such as portable radios. Moreover, making these interconnections complicates the assembly process, and creates the possibility of quality problems caused by PCB contamination and contact failure. Discrete controls also utilize mechanical contacts to achieve the control function. Such contacts degrade with time and use resulting in an unreliable control device.
Optical control devices which are well known in the art, have typically required a multiple number of light sources and/or a multiple number of light receptors. At least one light receptor is required for each control state. Thus, such conventional optical devices require premium board space and are expensive. Furthermore, conventional optical devices have not provided absolute position indication upon start up. In other words, such conventional optical devices only give relative information from an unknown state. Alternatively, optical control devices that measure the intensity of reflected light to an optical receiver are also well known and are of the type disclosed in U.S. Pat. No. 4,964,693 to Branan et al. Such a device requires appropriate control circuitry capable of measuring the intensity of the reflected light.
More particularly, U.S. Pat. No. 3,610,941 to West teaches a program control system having a glass or plexiglass rod with circumferential grooves which refract light out to photoelectric cells. The rod is illuminated by a light source disposed at one end of the rod. The photoelectric cells are energized in a controlled sequence by luminous portions of the respective grooves as the rod rotates. Since the rod is illuminated at one end by a light source enough space must be provided in order to house the light source. Furthermore, since circumferential grooves are provided on the rod to refract the light out of the rod, a further step is required of opaquing the rod in areas where light should not be refracted in order not to excite the photoelectric cells when so desired.
Since consumers demand smaller and more reliable control devices, a need exists for a reliable optical switch, as an absolute position indicator, that can be easily manufactured and consume only a small portion of the apparatus in which it is contained.